text: tolerance seems to differ between various marine organisms, as well as  tolerance at different life cycle stages (e.g. larva and adult). The first stage in the life cycle of marine calcifiers at serious risk from high  content is the planktonic larval stage. The larval development of several marine species, primarily sea urchins and bivalves, are highly affected by elevations of seawater p. In laboratory tests, numerous sea urchin embryos were reared under different  concentrations until they developed to the larval stage. It was found that once they reached this stage, larval and arm sizes were significantly smaller, as well as abnormal skeleton morphology was noted with increasing p.
  Similar findings have been found in  treated-mussel larvae, which showed a larval size decrease of about 20% and showed morphological abnormalities such as convex hinges, weaker and thinner shells and protrusion of mantle. The larval body size also impacts the encounter and clearance rates of food particles, and if larval shells are smaller or deformed, these larvae are more prone to starvation.  structures also serve vital functions for calcified larvae, such as defense against predation, as well as roles in feeding, buoyancy control and pH regulation.
  Another example of a species which may be seriously impacted by ocean acidification is Pteropods, which are shelled pelagic molluscs which play an important role in the food-web of various ecosystems. Since they harbour an aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic  emissions. Laboratory tests showed that calcification exhibits a 28% decrease of the pH value of the Arctic ocean expected for the year 2100, compared to the present pH value. This 28% decline of calcification in the lower pH condition is within the range reported for other calcifying organisms such as corals. In contrast with sea urchin and bivalve larvae, corals and marine shrimps are more severely impacted by ocean acidification after settlement, while they developed into the polyp stage. From laboratory tests, the morphology of the -treated polyp endoskeleton of corals was disturbed and malformed compared to the radial pattern of control polyps.
  This variability in the impact of ocean acidification on different life cycle stages of different organisms can be partially explained by the fact that most echinoderms and mollusks start shell and skeleton synthesis at their larval stage, while corals start at the settlement stage.  Hence, these stages are highly susceptible to the potential effects of ocean acidification. Most calcifiers, such as corals, echinoderms, bivalves and crustaceans, play important roles in coastal ecosystems as keystone species, bioturbators and ecosystem engineers. The food web in the arctic ocean is somewhat truncated, meaning it is short and simple. Any impacts to key species in the food web can cause exponentially devastating effects on the rest of the food chain as a whole, as they will no longer have a reliable food source. If these larger organisms no longer have any source of nutrients, they too will eventually die off, and the entire Arctic ocean ecosystem will be affected. This would have a huge impact on the arctic people who catch arctic fish for a living, as well as the economic repercussions which would follow such a major shortage of food and living income for these families.